Abstract

Striga species are parasitic weeds that seriously constrain the productivity of staples including cereals and legumes in Sub-Saharan Africa and Asia. In the eastern and central Africa region, Striga spp. infest as much as 40 million hectares of smallholder farmland causing total crop failure during severe infestation. As molecular mechanisms underlying resistance are yet to be elucidated, we undertook a comparative metabolome study using the Striga-resistant rice cultivar 'Nipponbare' and the susceptible 'Koshihikari'. We found that a number of metabolites accumulated preferentially in the Striga-resistant Nipponbare upon S. hermonthica infection. Especially, increased deposition of lignin, a phenylpropanoid polymer mainly composed of p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) aromatic units, around the site of interaction in Nipponbare was apparent. The increased deposition of lignin was accompanied by induction of the expression of corresponding enzymes encoding genes in the phenylpropanoid pathway. In addition, perturbing normal lignin composition by knocking down or overexpressing the genes regulating lignin composition i.e., p-COUMARATE 3-HYDROXYLASE or FERULATE 5-HYDROXYLASE, resulted in enhanced susceptibility of Nipponbare to S. hermonthica infection. These results demonstrate that enhanced lignin deposition, and the maintenance of the structural integrity of lignin polymers deposited at the infection site are crucial for post-attachment resistance against S. hermonthica.